Best potentiometer for an arm aplication

[Luan Motta]

Hi!
I'm developing a system for our robot. It's an arm, and we need to control the position of it by a potentiometer. We would like to know what is the better and more apropriated potentiometer to buy for this mechanism.

[RyanN]

Something in the 10KΩ range usually works pretty well.

You aren't very specific with the needs. How far does it need to turn? 90˚? 180˚? 270˚? 360˚? More?

From my experience so far in the 'real-world,' Bourns potentiometers are the gold-standard.

You may also like to take a look at US Digital Rotary Encoders, specifically the MA3

We had good luck with the MA3 in the past. It can output as a 10-bit (ignore this... it works great) analog value. In essence, it works the same as a potentiometer, but has no physical rotation limits. The voltage will go from 0V to 5V, then reset to 0V.

Next time, give us some more information. We're smart people here, but we can't read minds.

[DonRotolo]

To expand on the 10k recommendation, pots with higher values will tend to be too noisy.

Also be sure you use a Linear (B) taper pot, not an audio (A) taper.
We have had success with cheap pots from Mouser, but the encoders RyanN mentioned are more stable.

[Joe Ross]

We've used Vishay 534 series 10 turn pots for 4 out of the last 6 years without any problems or failures. We typically use 5k, except for last year when we used 10k connected to the Jaguar. They are $10-15, which is about the same as the equivalent Bournes.

Any pot is most linear in its center range. We typically try to use no more then 80% of the pot's range.

[Dan Oelke]

So does anyone have any pictures or descriptions of how they have physically connected a pot to an arm?

We would like to use this kind of a scheme this year, but have never done it before and so need some ideas on the best way to do the mechanical link between an arm and the pot.

Also - any good advice as to the kind of resolution we should be able to get?

[Joe Ross]

We use the mounting method described on page 7 of the following whitepaper. http://www.chiefdelphi.com/media/papers/1743

We've never tried to measure the resolution, as it's always been more then we needed. The A/D in the cRIO is 12 bit in the range of -10 to 10v, so from 0-5v, you get 10 bits (1024 steps).

[Dan Oelke]

Thanks Joe - that helps!

Yeah - figuring 1024 steps on say 300 degrees worth of turn would give about 1/3 of a degree per bit. Not bad - I would like a little better - mostly because I know we will be looking at the angle of our launcher which can be constrained to probably only 30 degrees worth of movement. Hmmmm - maybe there is a linear pot with much less turn ..... time to do some searching.

Any other ideas for mounting? I ask because we won't be using a motor to directly drive the ramp angle so we won't have a motor shaft to lock onto. I think I can see a way to do it, using a stiff wire to go between the arm and thru a hole/slot on the pot arm. But seeing something that has worked for someone else would be cool.

[trilogy2826]

Until something better not yet invented comes along, I will always spec in the AN8 sensor from Cherry (http://www.cherrycorp.com/english/se...n8_series.pdf).

It is a magnetic Hall effect rotary sensor that can be used with any two pole magnet. The output is effectively the same as a potentiometer. Major advantages are:
-non contact
-can be non concentric to a degree
-very robust
-360 infinite rotation (only senses 350 degrees)

2826 has been using these sensors in every robot since 2009 and we love them.

[Luan Motta]

Sorry, I was not very specific, but we need a 3V, 180 degrees, 10KΩ potentiometer.

We are programming the arm with a window motor in java. We are using the potentiometer as reference for the joystick. When the arm of the potentiometer is greater than joystick, the arm will decrease, and When lower, it will increase. Always watching the same degrees of the joystick.

If you guys recommend me a potentiometer that the voltage will go from 0V to 5V, it doesn't matter the voltage, but we would like to have a 3V.

I'll be grateful if someone pass me links to buy potentiometers.

[Ether]

Originally Posted by Luan Motta

If you guys recommend me a potentiometer that the voltage will go from 0V to 5V, it doesn't matter the voltage, but we would like to have a 3V.

A pot does not generate voltage. It just divides down the voltage you supply to it.

The max voltage out of a pot is a function of the voltage you supply to the pot.


Joe Ross recommended Vishay pots in post 4 of this thread.

[DonRotolo]

Originally Posted by Dan Oelke

maybe there is a linear pot with much less turn ..... time to do some searching.

Use mechanical means to turn 30 degrees into 225 degrees of mvement, such as gears (plastic works well)

Originally Posted by Luan Motta

Sorry, I was not very specific, but we need a 3V, 180 degrees, 10KΩ potentiometer.

If you guys recommend me a potentiometer that the voltage will go from 0V to 5V, it doesn't matter the voltage, but we would like to have a 3V.

Again, use mechanical means if 180 deg is desired, but IMHO 180 is plenty of rotation for a 270 pot.

As Ether noted: you connect one end of the pot to ground, the other end to whatever voltage you want (I very strongly recommend using the 5 volts from the sidecar) and the middle goes to an analog input. The voltage you read is proportional to the pot's position.

Have fun